Tangential bending and stretching of thin magnesium alloy sheets in warm conditions

The present work aims at studying the tangential bending process (wiping) and the combined effect of a bending and stretching stress on thin (0.7 mm) magnesium alloy (AZ31) sheets when working in warm conditions. The test equipment was designed in order to heat the sheet only in the bending region and to stretch the sheet after the wiping process; it was used for investigating the parameters affecting the stretch-bending state of stress in the sheet, quite common in the stamping process. A preliminary screening analysis over a large set of process parameter was performed using a full factorial design. As a result, only the effect of the temperature, the speed and the bend radius were further investigated according to a central composite design and using the springback factor and the maximum stretching load as response variables. The present work can give useful guidelines in the warm forming of AZ31 Mg alloy sheets in terms of key process parameters, fillet radii of the equipment, material stretch-bending strength (according to temperature, bending radius and speed) and precision of the final part (springback amount).